| International shipping is the main mode of transport in international trade. More than two-thirds of international trade is carried out by means of ocean-going shipping. Ship propulsion system is an important part of marine power plant, which plays a vital role on the vessel's normal navigation. As main components, the working state of diesel engine and gearbox affects directly the reliability and vitality of the ship. This article is intended to find a valid and economical method which can diagnose the diesel and gear box simultaneously. Based on the comprehensive analysis of research and application on diesel engine and gear box fault diagnosis from domestic and foreign research results, this article adopts the method of fault diagnosis based on torsional vibration signals from ship propulsion systems. Through simulation analysis, the appropriate criteria are obtained and verified by analyzing actual test data, the main research findings are as follows:(1) According to the structural characteristics of ship propulsion systems, based on parametric feature modeling technology, a parametric modeling system of marine propulsion system was established, which includes the components such as the linkage mechanism of diesel engine crankshaft, gear box, shaft and propeller. Every part of the system is independent from each other, and the entire propulsion system integration modeling may be achieved through positioning coordinates of every part. The procedure is performed in UG, where VC and Databases served as tools for secondary development. Models, with a wide range of common interface, can import to other analysis software such as ANSYS, MSC Patran, Adams, then subsequent analysis can be carried out. This system simplifies the modeling process of marine power plant for researchers, so that much more attention can be paid on the issue of analysis and research on structural performance of marine propulsion system.(2) For the study of ship's propulsion shafting, traditional method to build torsional vibration model of propulsion shafting is analyzed. Torsional vibration model for gears based on stiffness matrix unit can be derived from the differential equation of gear vibration which solves the problem that it is difficult to take fluctuate of transmission ratio for the entity model into account. Furthermore, some effort was put into the gear meshing coupling vibration models. By modeling the bending-torsional-longitudinal-swing coupling vibration system, meshing stiffness matrix formula was derived theoretically. The result on natural frequency for disc models from difference method is obtained from calculation and analysis, which revealing the results from simplified model are different from beam model and solid model, providing some useful ideas and methods to increase accuracy in the analysis of torsional vibration for propulsion shafting. The sensitivity of torsional vibration from the effect of stiffness and inertia is analyzed, and their influence on the natural frequency is assessed.(3) The excitation source for marine propulsion shaft during operation was briefly discussed. Based on the response analysis theory, the method of frequency response analysis and transient response analysis for shaft torsional vibration was given. In order to get the amplitude and phase characteristics during the fault of a certain cylinder, a 10,000 DWT River-Sea Cargo Ship was presented as an example. In this process, two kinds of fault were considered. The first one, marine engine failure, was simulated, which obtaining the frequency response characteristics such as vibration amplitude and phase in different harmonic order when the failure of each cylinder. The second one, marine gearbox failure, was performed by making faults in teeth for different gears, transient response characteristics will come out, similarly. Some research about the conditions when diesel engine and gearbox both work in failure was mentioned.(4) A lot of analysis was performed to look into the effect of gas excitation force and reciprocating inertia force on marine engine. A novel polar presentation method was introduced, which can be used to locate fault cylinder. When engine was forced by gas excitation force merely in simulation, torsional vibration signal for single-cylinder failure can be simulated and failure criterion in polar plot was given. At the same time, something about twin cylinder failure was mentioned, which expanded the applicability of polar presentation method.(5) For the experimental part of this thesis, power plant with MAN B&W 6L 16/24 and WP10-240 came into view, respectively. Plant with WP10-240 was taken as key object. There are some introductions about the basic condition of this test platform and the test scenario, from which the instantaneous angular speed (IAS) when every cylinder turn into failure were obtained. Besides, analysis about the angel characteristic during one cylinder failure and polar plot for plant with MAN B&W 6L 16/24 was given. It means that a complete analysis using polar presentation method was performed, which verified the effectiveness of this method.
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